## create a merge function that creates merge frequency as in Stata ##
## from user rwbuie at stackoverflow: https://stackoverflow.com/questions/30358401/is-there-a-way-to-create-statas-merge-indicator-variable-with-rs-merge ##

stata.merge <- function(x,y, name){
  x$df1 <- 1
  y$df2 <- 2
  df <- merge(x,y, by = name, all = TRUE)
  df$merge.variable <- rowSums(df[,c("df1", "df2")], na.rm=TRUE)
  df$df1 <- NULL
  df$df2 <- NULL
  df
  #print(table(df$merge.variable))
  
  ## return the merged dataframe
  return(df)
}